Magnetic-field-free separation and recovery of MXene-doped GO composites via dye-bridged reassembly in dye adsorption

Abstract

Dye wastewater, which poses serious threats to ecosystems and human health, is very difficult to treat. Graphene oxide (GO) has significant potential for dye adsorption. However, the practical application of GO in dye wastewater treatment is hindered by its high water solubility, which prevents its efficient separation and recovery after dye adsorption. In this study, we found that doping a small amount of MXene into GO induces composite dye-bridged reassembly during dye adsorption. The reassembled composite possesses favorable stability under external forces, thus enabling solid–liquid separation and material recovery without an external magnetic field. Notably, this dye adsorption-induced reassembly phenomenon was not observed in pure GO or pure MXene dye adsorption systems. The experimental results demonstrated that a small-fragmented GO/MXene composite with 20% MXene doping achieved optimal methylene blue (MB) adsorption and dye-bridged reassembly performance, with a maximum experimental adsorption capacity measured in practice of 883.17 mg g⁻¹. The MB removal capacity of the composite was maintained over a wide pH range, with dye-bridged reassembly preferentially occurring under acidic and weakly alkaline conditions (pH 3–9). Higher dosages enhanced MB removal but impaired the dye-bridged reassembly, whereas thermal annealing reduced the composite adsorption capacity but preserved its dye-bridged reassembly ability. Although the presence of cations hindered MB adsorption, they promoted reassembly efficiency, which was positively correlated with cation valence. A quantitative recovery of approximately 95% was achieved with the GO/MXene composite. The proposed strategy enables efficient and scalable dye removal and offers a new path for high-performance and sustainable dye wastewater treatment.